1. Field of Invention
The present invention relates to a roller temperature control method of an image forming apparatus by detecting the temperature of a roller of a fixing apparatus and performing heating control of the roller based on the detected temperature, and further relates to an image forming apparatus.
2. Related Art
In image forming apparatuses of electrophotography type, such as a copying machine, a printer and a facsimile, a toner image is formed on the surface of a photosensitive drum by forming an electrostatic latent image on the surface of the photosensitive drum, by supplying toner to the surface of the photosensitive drum from a development apparatus, and then by developing the electrostatic latent images on the surface of the photosensitive drum with the toner, and the toner image is fixed to recording paper by transferring the toner image to the recording paper from the photosensitive drum and by applying heat and pressure to the recording paper.
Among these image forming apparatuses, those that accommodate both color and monochrome are becoming more widespread, and the printing processing speed has been increased for both color and monochrome. More specifically, when using standard A4 size recording paper, the transport speed of the recording paper for color printing processes is set to 41 sheets/minute (a processing speed of 225 mm/sec) and the transport speed of the recording paper for monochrome printing processes is set to 70 sheets/minute (a processing speed of 350 mm/sec),
However, when printing is switched to color or the printing processing speed is increased, the maximum power consumption of an image forming apparatus becomes significantly large, and the maximum power consumption almost exceeds the normally allowable level of the commercial alternative current power, and this has been a significant problem.
In image forming apparatuses, the power consumption is the largest in a fixing apparatus that applies heat and pressure to recording paper. In this fixing apparatus, since heat and pressure are applied to the recording paper while it is sandwiched between a hot roller and a pressure roller, a heater for heating a roller is needed, and a large amount of power is consumed due to heat generation from the heater. In addition, when the printing process is in color or its speed is increased, the power consumption of the heater becomes exceptionally large.
Furthermore, since it is necessary to appropriately control the surface temperature of the hot roller and of the pressure roller, a built-in heater may be provided for this purpose within the hot roller and within the pressure roller, or an external heating apparatus may be provided so as to supplementarily heat the rollers. However, since the power consumption becomes extremely large such that it causes, for example, tripping of the breaker of commercial AC power if the heaters of the hot roller and the pressure roller as well as the heater of the external heating apparatus are simultaneously and fully used for heat generation, each heater needs to be appropriately controlled.
For example, in JP H08-220929A, the surface temperature of each roller is switch controlled in accordance with the thickness, size, transport direction, transport interval, and temperature of recording paper and others.
In addition, often times, the surface temperature of each roller is also switch controlled in accordance with the monochrome or color printing process, transport speed of recording paper and others.
Accordingly, the method for controlling the heater of each roller is complicated, and the control method for each heater is switched to no small extent.
However, when the control method for the heater of the hot roller and of the pressure roller as well as of the heater of the external heating apparatus is set to be switched in a complicated manner in accordance with the type and transport speed of recording paper or the printing process type like in the conventional way, the surface temperature of the rollers can sometimes experiences unexpected and inappropriate changes, which has caused fixing deficiencies.